Multiple and two-way reversible shape memory polymers: Design strategies and applications

Shape memory polymers (SMPs) are capable of changing their shapes in a pre-defined manner under a stimulus, and have gained considerable interest in the past decades. Although a number of stimulus-responsive SMPs have been developed, thermally-induced SMPs are still the most common. This review presents the concepts, the programming procedures, the molecular mechanism, classification, design strategies and the recent progress of thermally-induced SMPs, including dual, triple, multiple SMPs and two-way reversible SMPs (2W-SMPs) activated by direct and indirect heating method. Examples of the applications of these types of SMPs are also presented and discussed.